We define a listener method that makes the OpenFlow switches act as a simple hub. Then we call from the launch(), which is invoked at the start of the application.

Listing 10.6 gives a simple FTP connection test as follows:

#!/usr/bin/env python 
# Python Network Programming Cookbook, Second Edition -- Chapter - 10 
# This program is optimized for Python 2.7.12. 
# It may run on any other version with/without modifications. 
# Adopted from https://github.com/noxrepo/pox/blob/carp/pox/forwarding/hub.py 
# For more examples and tutorials:  
#   https://github.com/noxrepo/pox/tree/carp/pox 
 
from pox.core import core 
import pox.openflow.libopenflow_01 as of 
from pox.lib.util import dpidToStr 
 
log = core.getLogger() 
 
# The listener definition: A simple and stupid hub. 
def _handle_ConnectionUp (event): 
    msg = of.ofp_flow_mod() 
    msg.actions.append(of.ofp_action_output(port = of.OFPP_FLOOD)) 
    event.connection.send(msg) 
    # log the action. 
    log.info("Hubifying %s", dpidToStr(event.dpid)) 
 
 
# When the application is launched with POX. 
def launch (): 
    #Add a listener (defined above) to the pox.core openflow. 
    core.openflow.addListenerByName("ConnectionUp",
     _handle_ConnectionUp) 
    log.info("Hub is running.") 

The execution of this recipe prints the following output:

$ ./pox.py log.level --DEBUG 10_6_sdn_pox
POX 0.2.0 (carp) / Copyright 2011-2013 James McCauley, et al.
INFO:10_6_sdn_pox:Hub is running.
DEBUG:core:POX 0.2.0 (carp) going up...
DEBUG:core:Running on CPython (2.7.12/Nov 19 2016 06:48:10)
DEBUG:core:Platform is Linux-4.8.0-58-generic-x86_64-with-Ubuntu-16.04-xenial
INFO:core:POX 0.2.0 (carp) is up.
DEBUG:openflow.of_01:Listening on 0.0.0.0:6633